This invention is directed to a communications channels evaluation system and in particular to an evaluation system for point-to-point high frequency communication systems.
Uncertainty exists in realizing the overall potential of high frequency communications systems. Equipment parameters can be controlled by the operating personnel but factors such as propagation conditions over the transmission path, the presence of co-channel interference on a particular channel and the ability to select the optimum traffic frequency at any given time are normally beyond their control. Yet these factors are vital in maintaining circuit reliability at its fullest potential.
The operational approach to high frequency communications has conventionally been to assign a family of frequencies to a particular circuit which are used at the discretion of the operating personnel, the traffic frequency at any given time being selected either on the basis of long term frequency predictions or operational experience. As high frequency propagation is subject to the vagaries of the ionospheric characteristics present at any given time over the propagation path, there is no guarantee that the optimum channel is being used or that communications can be successful using these conventional methods for circuit control. Furthermore there is no means for the operating staff to assess the relative performance of assigned channels without a lengthy procedure of trial and error.
For a simplex communications system wherein the same frequency is used for communication in both directions, the above problems have been obviated by channel evaluation systems such as the one described in U.S. patent Ser. No. 3,543,161 which issued on November 24, 1970 to Hatton et al. However, this system is not suitable for point-to-point high frequency communications systems wherein high traffic density is supported by simultaneous transmission in both directions on two different frequencies, each frequency being selected from a separate set of frequency assignments.